This invention relates generally to hydraulically-actuated systems used with internal combustion engines, and more particularly to a variable-delivery, fixed-displacement pump of a high pressure hydraulically-actuated system.
Axial piston pumps are known to be used in hydraulically-actuated fuel injection systems. The efficient operation of such pumps is significant to the overall operation of the engine. Moreover, the ability of such pumps to operate free of maintenance is important to reduce downtime of the system.
U.S. Pat. No. 6,035,828 to Anderson et al. describes a fixed displacement, variable delivery axial piston pump for a hydraulically-actuated fuel injection system. In the Anderson et al. system, a high pressure common rail supplies hydraulic fluid to a plurality of hydraulically-actuated fuel injectors mounted in a diesel engine. The hydraulic fluid received in the common rail is pressurized by the fixed displacement axial piston pump that is driven directly by the engine. The pump includes a plurality of pistons disposed in parallel about the central longitudinal axis of the pump, and reciprocation of the pistons is achieved by the rotation of an angled camming surface or swash plate that is biased against a proximal end of the pistons. Displacement of the pump is varied by a control actuator that selectively varies the amount of pressurized fluid supplied to the pump outlet during the discharge stroke of each piston.
While the Anderson et al. pump performs well in operation, the amount of fluid pushed through the check valve to the common rail is varied by allowing leakage of pressurized fluid from the pumping chamber via spill ports. Some of the work used to pressurize the fluid in the pumping chamber is eventually lost through this leakage of fluid through the spill ports. Also, the sleeves that selectively block the spill ports have a reciprocation distance that may require an expensive actuator. The reciprocation of the sleeves may also lead to failure of the sleeves or other associated components that requires maintenance or replacement.
The present invention provides an axial piston pump that avoids some or all of the aforesaid shortcomings in the prior art.
In accordance with one aspect of the invention, a pump includes a pump housing, a rotating shaft extending through the pump housing, a plurality pistons, and a plurality of control sleeves. Each piston may be at least partially, slidably contained within a respective piston sleeve. The pistons may also be operably coupled to the rotating shaft such that rotation of the shaft rotates and reciprocates the pistons. Each control sleeve may be slidably disposed on a respective one of the piston sleeves and operable to selectively vary the amount of fluid delivered by the pump.
According to another aspect of the present invention, a method of delivering an amount of pressurized fluid from a pump includes reciprocating a plurality of pistons in a plurality of respective piston sleeves through a retracting stroke and a compression and delivery stroke. The method also includes operably moving a control sleeve to selectively vary a flow of fluid through a sleeve port in the piston sleeve during the retracting stroke so as to vary the amount of fluid delivered by the pump.
According to yet another aspect of the present invention, a hydraulically actuated system includes a pump including a rotating shaft, a plurality pistons, and a plurality of control sleeves. Each piston may be at least partially, slidably contained within a respective piston sleeve, and the pistons may be operably coupled to the rotating shaft such that rotation of the shaft rotates and reciprocates the pistons. Each control sleeve may be slidably disposed on a respective one of the piston sleeves and being operable to selectively vary the amount of fluid delivered by the pump. The system also includes a high pressure rail connected to the pump, at least one hydraulically actuated fuel injector connected to the high pressure rail, and an electronic control module configured to control the control sleeves.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.